Gasoline, C5-11 hydrocarbons, is a kind of necessary transportation fuels for the development of modern society. At present, gasoline is produced mainly from petroleum by the process of direct distillation and catalytic cracking of crude oil, however, due to the limitation of petroleum resource reserve, developing the gasoline production technology from nonpetroleum resources is already becoming research targets of lots of countries. CO2, as the cheapest and most abundant resources of C1 compounds, has a plentiful of storage on the earth. Along with the continuous development of human society and the rapid increase of consumption of fossil energy resources, CO2 concentration in atmosphere increases sharply, which not only intensifies the greenhouse effect, but also results in the huge waste of carbon resources. The CO2 derived from industrial waste gases or captured from atmosphere and the hydrogen derived from renewable energy sources could be used as feedstocks for the catalytic conversion of CO2 to liquid hydrocarbons, such process has the significance to solve not only the climate change but also energy crisis, that peoples encountered in modern society.
The research results indicate that, the hydrocarbons synthesis from CO2 hydrogenation generally includes the next two steps: first, CO2 react with H2 to form CO via RWGS (Reverse water gas shift) reaction, and then, CO conversion to hydrocarbons via Fischer-Tropsch synthesis (F-T synthesis) reaction. For the traditional F-T synthesis of CO hydrogenation to hydrocarbons, the product selectivity follows the rules of Anderson-Schulz-Flory (ASF) distribution. According to ASF rules of hydrocarbon distribution, the content of gasoline hydrocarbons (C5-11 hydrocarbons) in hydrocarbon products is not more than 45%. Different from that in CO hydrogenation process, there exists a low C/H ratio on the surface of catalyst in CO2 hydrogenation process due to the slow adsorption of CO2 on the catalyst surface. Such phenomena in CO2 hydrogenation is beneficial to hydrogenation of adsorbed species and decrease of probability for product chain growth, and thus selectivity to methane is further raised while the formation of long chain hydrocarbons becomes more difficult. Therefore, about the present literatures' studies on CO2 hydrogenation, the target products concentrate on small molecular weight compounds such as methanol (e.g. CN201110006073.8), dimethyl ether (e.g. CN201410495290.1), methane (e.g. CN201210444697.2), and light olefins (e.g. CN201510102620.0), a few studies on long chain hydrocarbon synthesis from CO2 hydrogenation. The literature (Y Tan et al. Ind. Eng. Chem. Res. 38 (1999) 3225-3229) reported that 52% of C5+ hydrocarbons in total hydrocarbons could be obtained at 19.5% of CO2 conversion, however, 57.4% of selectivity to byproduct CO exist in this process, the yield of C5+ hydrocarbons is very low. M. Fujiwara et al. (Appl. Catal. B: Environ 179 (2015) 37-43) recently found that over the hybrid catalysts, comprised of Cu—Zn—Al methanol synthesis catalyst and modified HB zeolite, C2+ hydrocarbons could be obtained from CO2 hydrogenation, however, selectivity to byproduct CO is higher than 50%.
Altogether, although some progresses have been made in the studies on CO2 hydrogenation to gasoline-range hydrocarbons, selectivity to gasoline-range hydrocarbons, the target products, is still low, and selectivities to CO and CH4 are still high, which is far away from the requirement of practical use. So, the urgent task for CO2 conversion to gasoline is to find a high efficient process for CO2 hydrogenation to gasoline with high CO2 conversion and high selectivity to gasoline.